neoadjuvant chemotherapy in stage III and IV ovarian cancer is given in 3-4 cycles with patients who R0 surgical resection is less likely to occur, in this study will assess total neoadjuvant chemotherapy 6 cycles then interval debulking surgery (experimental arm) versus 4 cycles then interval debulking surgery (control arm) in patients who achieve partial response or stationary disease by imaging after 3- 4 cycles of neoadjuvant chemotherapy, investigators'' primary end points will be event free survival, safety and tolerability and time to relapse, our secondary end points will be overall survival and surgical morbidity and mortality

Inclusion Criteria:

1. > 18 years of age
2. Recently diagnosed with stage III and IV OC
3. Patients eligible for Platinum-based CTH
4. Patients have PR or SD after 3-4 cycles of NACT

Exclusion Criteria:

1. Relapsed ovarian cancer
2. patients ineligible for Platinum-based CTH
3. Patient not candidate for IDS
4. stage I, II OC
5. Patients progressed after 3 cycles

7-Patients do not tolerate CTH